on the mk4 calliper you have to rotate the piston as well as push it in to the calliper. if you are lucky or using brand new callipers you proberly can do it with a g clamp but i would advise using a reset tool as it does the job in about 20 seconds flat and doesnt damage the exterior of the calliper if you have painted them.
why stuggle if you can get the right tool for the job
plus when you change pads and discs you will need it then any way. tell everbody you have one and lend it out to them for beer.... always a winner a find?
